Number Of Acrocentric Chromosomes Research Articles

Evolution of trans-Andean endemic fishes of the genus Cheirodon (Teleostei: Characidae) are associated with chromosomal rearrangements

BackgroundAmong Neotropical fishes, the family Characidae is highly diverse and speciose and its taxonomy is not completely resolved. In Chile, the family is represented by five species, all within the genus Cheirodon, of which C. pisciculus, C. galusdae, C. kiliani, and C. australe are endemic, while C. interruptus is introduced. We compared chromosomal markers in order to appreciate the taxonomy and evolution of these trans-Andean fishes.ResultsThe specimens were photographed in stereomicroscope to observe the ventral protrusive teeth and cusps for morphological analysis and species identification. All of the species analysed had equally diploid chromosome number 2n = 50, with karyotypes dominated by high number of acrocentric chromosomes as compared to those of other members of Cheirodontinae. The distribution of heterochromatin was inconspicuous and was similar in all the species. The number of active NORs (nucleolus organizer regions) was polymorphic, with the greater number of them in C. kiliani and C. galusdae. The location of 5S and 18S rDNA ranged in number and position, showing two sites in different chromosomes. The fluorescent in situ hybridization with telomeric probe did not reveal interstitial sites in all analysed species.ConclusionsThe comparative analysis of karyotypes and morphological markers revealed a biogeographic pattern of distribution, with the species that occur in the southern region forming one group and those in central and northern Chile forming another.

Reorganization of species genomes during evolutionary specialization of taxa

The study of genetic aspects of speciation and adaptation revealed several genetic parameters that distinguish evolutionarily labile (with a low level of specialization) species that are “generators” of speciation and evolutionarily conservative (highly specialized) species. In the evolutionary development of a taxon in the horizontal direction (cladogenesis or adaptive radiation), the features of low genome specialization at each step of the speciation are substituted gradually for alternative (evolutionarily conservative) ones, which are most pronounced in terminal species. In speciation, the number of acrocentric chromosomes (Robertsonian fusion) is reduced; polyploidy takes place—the emergence of fixed chromosomal rearrangements and increase in their number, as well as “dispersion” of heterochromatin and mobile genetic elements from their chromocenters and centromeric regions to the lateral regions of chromosomes. In addition, the recombination is limited, chromosomal (inversion) polymorphism forms, and the areas of chromosomal attachment to the nuclear envelope are expanded. The identified parameters of the structural and functional organization of the genome in species that are “generators” of speciation and in inert (conservative) species in terms of speciation characterize the evolutionary heteropotential of species genomes and nonequivalence of species with respect to natural selection. The first species seem to generate clusters of affiliated species, and the second create their own system of genetic adaptation (chromosomal polymorphism). They usually become eurybiontic species, which terminate phyletic lines.

Cytogenetic description of Bunocephalus doriae Boulenger, 1902 (Siluriformes: Aspredinidae) from the Paraná River (Misiones, Argentina)

In this work, Bunocephalus doriae was cytogenetically analyzed. A karyotype with a diploid number of 2n= 50 comprising 6m, 10sm, 6st, and 28a (FN= 72) chromosomes was observed. The occurrence of an asymmetric karyotype with a large number of acrocentric chromosomes distinguishes this species from others the Order Siluriformes. An exclusive character observed is the first pair of subtelocentric as the largest chromosome pair of the complement. NORs detected using AgNO3 were located in the terminal regions, on the short arm of a subtelocentric chromosome pair (pair 11), in a secondary constriction. C-banding revealed heterochromatic centromeric regions on several chromosomes of the complement after C-banding. This is the first cytogenetic description of this species and the first cytogenetic report on a member of the family Aspredinidae.

DETECTION OF PREMATURE SEGREGATION OF CENTROMERES IN PERSONS EXPOSED TO IONIZING RADIATION

We have analyzed the frequency of premature centromeric division (PCD) in medical personnel professionally exposed to low doses of radiation. They had chromosome aberrations (CAs) involving dicentric chromosomes, ring chromosomes, acentric fragments, chromosome breaks, and chromatid breaks. The study included 30 exposed subjects and 23 controls who were each analyzed by a conventional cytogenetics procedure and subsequently by fluorescent in situ hybridization (FISH). The latter was applied particularly in order to verify PCD in a specific chromosome (chromosome 18) in both metaphases and interphase nuclei. The results revealed a significant difference (p < 0.001) in frequencies between the two groups (exposed and controls) for all the observed variables (CAs), metaphases with PCD (MPCD), total number of chromosomes with PCD (TPCD), number of PCD metaphases in acrocentric chromosomes (MAPCD), and the total number of acrocentric chromosomes with PCD (TAPCD). The doses of ionizing radiation absorbed by the subjects' bodies were measured with thermoluminescent dosimeters once a month during the duration of occupational exposure. They were expressed in mSv, as mean annual effective doses for the period of exposure. The Spearman rank test showed a high positive correlation between total life effective dose and frequency of CAs and PCD. Based on the results obtained in this study, we suggest that PCD, as a phenomenon manifesting chromosomal instability (CIN), should be considered as a suitable cytogenetic biomarker for individuals occupationally exposed to ionizing radiation.

Cytotaxonomy and karyology of the tribe Otiorhynchini (Coleoptera: Curculionidae)

A cytogenetic study of bisexual species belonging to the genera Cirrorhynchus, Dodecastichus and Otiorhynchus is presented in order to confirm their taxonomic position. The karyotype characterization was accomplished by an analysis of mitotic and meiotic chromosomes after differential staining, namely by C-banding, silver impregnation, DAPI and CMA3. A review of the cytogenetic data for the tribe Otiorhynchini contributed to knowledge of chromosomal evolution in this group. An investigation of five of the species studied showed some similarities such as a sex chromosome system of "parachute type" (Xyp), the presence of 10 autosomal bivalents (2n = 22) and heterochromatin localized around centromeres. These observations are similar to those already described for Otiorhynchini species, and confirm the karyological conservatism of this weevil group. In contrast, another species Cirrorhynchus kelecsenyi has an additional four autosomal bivalents (n% = 14 + Xyp, 2n = 30), which differs considerably from the chromosomal homogeneity of the other genera. Karyotypic evolution in this species was achieved most probably by increasing the number of chromosomes by centric fissions, resulting in variation in the number of acrocentric chromosomes. DAPI-positive and CMA3-negative reactions of heterochromatic DNA in all the species studied suggest that it has an AT-rich composition. Impregnating chromosomes with silver nitrate reveals NORs on one pair of autosomes, and probably argentophilic material in the interspace between the X and y sex chromosomes. The karyological findings support the taxonomical revision of Otiorhynchini based on morphological characters.

Cytogenetic studies in Brazilian marine Sciaenidae and Sparidae fishes (Perciformes)

Fishes from the families Sciaenidae and Sparidae, the former comprising coastal species associated with shallow waters on the continental shelf and the latter composed of typically marine species, are of significant economic value. Karyotypic data are available for about 20% of the total number of species in these groups. In the present study, cytogenetic analyses were carried out in three Sciaenidae species, Menticirrhus americanus, Ophioscion punctatissimus and Pareques acuminatus, as well as in the sparid fish, Archosargus probatocephalus, using conventional staining (Giemsa) and Ag-nucleolar organizer regions (NORs) and C-banding techniques. The diploid values (2n) and number of chromosome arms were equal to 48 in all species analyzed. NORs were located at pericentromeric positions, equivalent to large heterochromatic blocks, in M. americanus (1st pair), O. punctatissimus (10th pair), P. acuminatus (2nd pair), and A. probatocephalus (3rd pair). Heterochromatin was detected at the centromeric position in most chromosome pairs, being more conspicuous among Scianidae members. The remarkable karyotypic conservativeness detected in these species is similar to that observed in other perciform groups previously studied, regarding both the number of acrocentric chromosomes and NOR location. However, unusual events of heterochromatinization seem to have taken place along the karyotypic evolution of members of the family Sciaenidae. For the family Sparidae, distinct cytotypes between samples of Northeast Brazil and those previously analyzed on the southeastern coast were identified, suggesting that putative biogeographic barriers could be present throughout both regions on South Atlantic coast.

Cytogenetic studies on Apareiodon affinis (Pisces, Characiformes) from Paraná river basin: sex chromosomes and polymorphism.

Comparative cytogenetic studies were carried out on Apareiodon affinis from an important hydrographic system at South America, the Paraná river basin. Two distant regions were chosen, which were separated by Guaíra Falls (formerly Sete Quedas); the region in the upper part of the hydrographic basin is called Upper Parana (Brazil), whereas and the other in the lower part is called Lower Parana (Argentina). Individuals from Upper Parana have diploid numbers of 2n = 54 (NF= 108) for males and 2n = 55 (NF = 110) for females, showing female heterogamety with a ZZ/ZW1W2 multiple sex chromosomes system that is endemic for the region. In different localities at Lower Paraná, the specimens presented diploid number of 2n = 54 for both sexes, without any sex chromosomes heteromorphism. However, they have an accentuated polymorphism characterized by variation in number of acrocentric chromosomes, constituting something new for family Parodontidae. The most likely hypothesis to explain the origin of such polymorphism is based on successive pericentric inversions giving rise to acrocentric chromosomes. Thus, it was possible to detect 10 cytotypes along the Lower Parana basin. Such chromosomal variations possibly are the consequence of an adaptative process. Our data probably indicate the occurrence of distinct species in each region that share the same denomination.

Karyological differences among Tenebrionidae (Coleoptera)

Karyotypes obtained from spermatogonial metaphases of 20 tenebrionid species have been surveyed. The range of chromosome numbers is from 2n=16 to 2n=26, but only five species deviate from 2n=20, which is the modal and most primitive number of the family. Only the tribe Akidini shows a clear relationship between chromosome number (2n=16) and taxonomic group, while in the other species this relationship is not apparent. The mean total complement lengths in eleven species vary about twofold and the number of chromosome arms (NF) from 23 to 50. Some congeneric species ofTentyria, Hegeter andErodius displayed slight differences in the number of acrocentric chromosomes.

Systematics and Distribution of Two Chromosome Forms in the Southern Grasshopper Mouse, Genus Onychomys

Chromosomes from 61 individuals representing 20 populations currently referable to Onychomys torridus were examined from Arizona, New Mexico, and Texas. Two distinct karyotypes were observed. In both chromosome forms the diploid number was 48. The principal differences reside in the morphology of biarmed chromosomes and number of acrocentric chromosomes. A contact zone between the two cytotypes was located in southwestern New Mexico. Based on karyotypes, no hybrid nor backcross individual was detected. These data indicate that two species have been included under the name O. torridus . The name arenicola is the oldest available name and is herein raised to specific rank. A morphometric analysis using 12 cranial and six external measurements was carried out on a total of 363 specimens representing both cytotypes. Age, secondary sexual, and geographic variation were analyzed. A final discriminant analysis showed significant separation between the two species.

Quantitative studies on the arrangement of human metaphase chromosomes. V. The association pattern of acrocentric chromosomes in human meningiomas after the loss of G and D chromosomes.

The association pattern was studied in 2715 mitoses of 90 meningiomas with different numbers of acrocentric chromosomes. In cells with monosomy 22, a significant increase of mitoses with associations was observed in comparison to cells with a normal karyotype. The number of associating acrocentric chromosomes was highly significantly increased. This surplus was not only caused by a highly significant increase of associating G chromosomes but also of D chromosomes. The loss of further acrocentric chromosomes had no significant influence on the number of mitoses with associations or the number of associating chromosomes. Based on the well-known correlations between the nucleolus organization and the association pattern, the results seem to indicate a compensation mechanism among the nucleoles organizing regions (NOR's) which keeps the supply of nucleolar material constant and simultaneously causes a higher association tendency between the remaining acrocentric chromosomes. The increase of associations in the 22 monosomic cells was interpreted as a overcompensation after the loss of only one NOR.

Localization of ribosomal RNA genes on human acrocentric chromosomes.

Clonal derivatives of a human heteroploid cell line, with different numbers of acrocentric chromosomes, show different rDNA contents. A linear relationship has been found between the rDNA content and the relative mass of the acrocentric chromosomes (D+G) expressed as the ratio between the mass of their DNA and the mass of the DNA of the whole chromosomal complement. The results suggest that human rRNA genes are located exclusively on the chromosomes of the groups D and G and that all these chromosomes contain rRNA genes.

The association of acrocentric chromosomes in 1000 normal human male metaphase cells

Associations among the acrocentric chromosomes of man were first described by FergusonSmith & Handmaker (1961) and Harnden (1961). Various investigators have suggested that such associations, in conjunction with other prominent heteropycnotic secondary constrictions, play a role in the organization of nucleoli (Schultz & St Lawrence, 1949; Ohno et al. 1961; Hungerford, 1964 ; Ferguson-Smith, 1964). Participation of the acrocentric chromosomes in such associations has been postulated to increase the risk of non-disjunction with subsequent trisomic conditions of groups D and G (Harnden, 1961; Ferguson-Smith & Handmaker, 1961). In fact, several families possessing chromosomally abnormal individuals have been purported to exhibit possible ‘increased satellite association’ (Tips et al. 1964; Kiossoglou et al. 1964; Lyons, Thompson & Bigley, 1966; Zellweger, Abbo & Cuany, 1966; Abbo, Zellweger & Cuany, 1966). However, studies of this type have not been too well defined and in some cases both cytogenetically normal and abnormal individuals have been compared directly (Van Brink, Los & Nienhaus 1962; Froland & Mikkelsen, 1964; Bishun, 1966; Zellweger et al. 1966; Abbo et al. 1966). Such comparisons pose difficulties since the number of acrocentric chromosomes may not be the same in each case, e.g. trisomic and normal individuals. In addition, population data from a large series of normals on the frequency and distribution of satellite associations are meagre. In this paper, we present data on various aspects of satellite associations, in the hope that such results might form a basis for comparison between normal individuals and persons with abnormal cytogenetic constitutions.